文摘
A carbon-coated Mg<sub>0.5sub>Ti<sub>2sub>(PO<sub>4sub>)<sub>3sub> polyanion material was prepared by the sol–gel method and then studied as the negative electrode materials for lithium-ion and sodium-ion batteries. The material showed a specific capacity of 268.6 mAh g<sup>–1sup> in the voltage window of 0.01–3.0 V vs Na<sup>+sup>/Na<sup>0sup>. Due to the fast diffusion of Na<sup>+sup> in the NASICON framework, the material exhibited superior rate capability with a specific capacity of 94.4 mAh g<sup>–1sup> at a current density of 5A g<sup>–1sup>. Additionally, 99.1% capacity retention was achieved after 300 cycles, demonstrating excellent cycle stability. By comparison, Mg<sub>0.5sub>Ti<sub>2sub>(PO<sub>4sub>)<sub>3sub> delivered 629.2 mAh g<sup>–1sup> in 0.01–3.0 V vs Li<sup>+sup>/Li<sup>0sup>, much higher than that of the sodium-ion cells. During the first discharge, the material decomposed to Ti/Mg nanoparticles, which were encapsulated in an amorphous SEI and Li<sub>3sub>PO<sub>4sub> matrix. Li<sup>+sup> ions were stored in the Li<sub>3sub>PO<sub>4sub> matrix and the SEI film formed/decomposed in subsequent cycles, contributing to the large Li<sup>+sup> capacity of Mg<sub>0.5sub>Ti<sub>2sub>(PO<sub>4sub>)<sub>3sub>. However, the lithium-ion cells exhibited inferior rate capability and cycle stability compared to the sodium-ion cells due to the sluggish electrochemical kinetics of the electrode.